The present invention relates to ceramic fiber tile insulation components for the protection of a reusable launch vehicle such as the space shuttle.
Reusable launch vehicles (RLVs), such as the space shuttle, repeatedly travel into or beyond the Earth""s upper atmosphere and then return to the Earth""s surface. During flight, the RLVs experience extreme temperatures, ranging from xe2x88x92250xc2x0 F. while in orbit to nearly 2900xc2x0 F. upon reentry to the atmosphere. Because of the extreme temperatures, the vehicle and its contents must be protected by a thermal protection system.
Thermal protection systems for RLVs are constructed from a large number, usually several thousand, of insulative tiles. The tiles function to insulate the vehicle from the environment and to radiate and reflect heat away from the vehicle. In addition to protecting the vehicle from environmental heat sources, the insulative tiles also provide protection from localized heating from the vehicle""s main engines, rocket boosters, and directional thrusters.
A currently preferred insulative tile material is alumina enhanced thermal barrier, AETB. AETB is a rigid, three-component tile material comprising silica fibers, alumina fibers, and aluminoborosilicate fibers. AETB is a preferred insulative material because of its low thermal conductivity, low coefficient of thermal expansion, and its ability to receive reaction cured glass (RCG) and toughened unipiece fibrous insulation (TUFI) coatings, which further increase its insulative properties.
AETB is produced in densities ranging from about 8 lbs/ft3 to about 20 lbs/ft3, denominated AETB-8, AETB-20, etc. In general, lower densities of tile are preferred because they have lower thermal conductivity and tend to better insulate the vehicle. However, low density AETB cannot be used on vehicle surfaces which experience the hottest temperatures, those near 2900xc2x0 F., due to the tendency of the low density tile to slump, or shrink, which requires replacement of the tile after use.
High temperature applications call for the use of high density AETB, such as 16 lbs/ft3 or 20 lbs/ft3, which is able to resist slumping but results in higher thermal conductivity and adds undesired weight to the vehicle.
What is needed is a material which has the exceptional thermal conductivity properties of AETB-8 and has the ability to withstand temperatures up to about 2900xc2x0 F. without degradation.
A multi-layer alumina enhanced thermal barrier tile and method of making the tile are therefore provided that exhibit the high strength and high temperature durability of high density AETB tile while exhibiting the superior insulative properties of low density AETB. The invented multi-layer tile achieves the advantages of both high density and low density AETB by bonding a layer of the low density AETB to a layer of the high density AETB to form a unitary multi-layer tile material. When used on a reusable launch vehicle with the high density AETB layer facing the outer mold line, the high density AETB layer of the tile resists slumping in the high temperature environment while the low density AETB layer, facing the inner mold line, provides superior insulative properties without the need to endure extremely high temperatures that are absorbed by the high density layer. Use of a low density layer also advantageously reduces the overall weight of the tile.
The multi-layer tile material is produced from different density AETB materials which are produced by conventional methods. The insulation layers are bound together by a high strength, high temperature alumina or silica binder having a coefficient of thermal expansion similar to that of the insulation layers. Use of the multi-layered AETB tile allows the problems of tile slumping and of insufficient heat management to be overcome.